This project addresses genetic heterogeneity in endothelial gene expression. Our overarching hypothesis is that the clinical phenotype of human vascular diseases will be influenced significantly by inherited differences in gene expression by endothelial cells. The unique combination of two relatively new technologies allows us to actually test this concept, directly and in humans: reporter endothelial cells can be obtained from peripheral blood sampling in the form of blood outgrowth endothelial cells (BOEC), and endothelial gene expression can be monitored by microarray profiling. This initial test of the hypothesis will focus on sickle anemia, a "single gene" disorder in which two very distinct clinical phenotypes can be reliably identified: at-risk for stroke versus not-at-risk for stroke; the at risk-group will be subdivided into those with versus those without moya moya. W e hypothesize that adolescents with HbSS who are at-risk for stroke (n=25) will exhibit different endothelial polymorphisms than the sickle subjects who are not-at-risk for stroke (n=25 each); we also hypothesize that at-risk subjects with moya moya (n=25) will exhibit different polymorphisms from those without moya moya (n=25). 25 non-sickle race and age matched adolescents will serve as controls. In Aim #1, microarray profiling of BOEC gene expression will be used to identify constitutive endothelial gene expression. In Aim #2, we will in parallel perform cell biologic experiments to examine for exaggerated endothelial responsiveness of several types felt to be high-probability for involvement in the stroke phenotype. In Aim #3 we will verify significance of candidate gene or response pathways implicated in Aims #1 and #2. In Aim #4, we will use data from a separate ongoing SNP study that looks for SNP associations with sickle stroke, to inform microarray analysis and thereby combine power of the two approaches.